Volume 63, Issue 3 - Highlight: Textile Engineering & Regenerative Medicine

With over 150,000 implantations performed over the world, transcatheter aortic valve replacement (TAVR) has become a surgical technique, which largely competes with open surgery valve replacement for an increasing number of patients. The success of the procedure favors the research toward synthetic valve leaflet materials as an alternative to biological tissues, whose durability remains unknown. In particular, fibrous constructions have recently proven to be durable in vivo over a 6-month period of time in animal sheep models. Exaggerated fibrotic tissue formation remains, however, a critical issue to be addressed. This work investigates the design of a composite fibrous construction combining a woven polyethylene terephthalate (PET) layer and a non-woven PET mat, which are expected to provide, respectively, strength and appropriate topography toward limited fibrotic tissue ingrowth. For this purpose, a specific equipment has been developed to produce non-woven PET mats made from fibers with small diameter. These mats were assembled with woven PET substrates using various assembling techniques in order to obtain hybrid fibrous constructions. The physical and mechanical properties of the obtained materials were assessed and valve samples were manufactured to be tested in vitro for hydrodynamic performances. The results show that the composite fibrous construction is characterized by properties suitable for the valve leaflet function, but the durability of the assembling is however limited under accelerated cyclic loading.

Electro-spinning is widely used in tissue-engineered applications mostly in form of non-woven structures. The development of e-spun yarn opens the door for textile fabrics which combine the micro to nanoscale dimension of electro-spun filaments with three-dimensional (3D) drapable textile fabrics. Therefore, the aim of the study was the implementation of a process for electro-spun yarns. Polylactic acid (PLA) and polyethylene glycol (PEG) were spun from chloroform solutions with varying PLA/PEG ratios (100:0, 90:10, 75:25 and 50:50). The yarn samples produced were analyzed regarding their morphology, tensile strength, water uptake and cytocompatibility. It was found that the yarn diameter decreased when the funnel collector rotation was increasd, however, the fiber diameter was not influenced. The tensile strength was also found to be dependent on the PEG content. While samples composed of 100% PLA showed a tensile strength of 2.5±0.7 cN/tex, the tensile strength increased with a decreasing PLA content (PLA 75%/PEG 25%) to 6.2±0.5 cN/tex. The variation of the PEG content also influenced the viscosity of the spinning solutions. The investigation of the cytocompatibility with endothelial cells was conducted for PLA/PEG 90:10 and 75:25 and indicated that the samples are cytocompatible.

Electrospun polyurethane based nanocomposite scaffolds were fabricated by mixing with indhulekha oil. Scanning electron microscope (SEM) portrayed the nanofibrous nature of the composite and the average diameters of the composite scaffold were smaller than the pristine scaffolds. The fabricated scaffold was found to be hydrophobic (114°) due to the inclusion of indhulekha oil, which was displayed in contact angle measurement analysis. The fourier transform infrared spectroscopy (FTIR) results indicated that the indhulekha oil was dispersed in PU matrix identified by formation of hydrogen bond and peak shifting of CH group. The PU/indhulekha oil nanocomposite exhibits a higher decomposition onset temperature and also residual weight percentage at 900°C was more compared to the pure PU. Surface roughness was found to be increased in the composite compared to the pristine PU as indicated by the atomic force microscopy (AFM) analysis. In order to investigate the blood compatibility of electrospun nanocomposites the activated partial thromboplastin time (APTT) assay, prothrombin time (PT) assay and hemolytic assay were performed. The blood compatibility results APTT and PT revealed that the developed nanocomposites demonstrated delayed clotting time indicating the anticoagulant nature of the composite in comparison with the pristine PU. Further, it was also observed that the hemolytic index of nanocomposites was reduced compared to pure PU suggesting the non-hemolytic nature of the fabricated scaffold. Hence, the fabricated nanocomposites might be considered as a potent substitute for scaffolding damaged tissue due to their inherent physicochemical and blood compatibility properties.

The development of scaffolds featuring spatiotemporal controlled release of drugs is highly desirable. The goal of this study is to construct an inhomogeneous scaffold with gradient pore structure from top layer to bottom layer. The scaffolds were prepared using bioglass (BG), phosphatidylserine (PS) and steroidal saponins (SS) loaded collagen (COL) microparticles as the main components. The resulting scaffold constructs were characterized in terms of their morphology, drug release kinetics and mechanisms, as well as macroscopic form stability and mechanical properties. Pore interconnectivity and graded distribution were demonstrated using scanning electron microscopy (SEM). Such constructs have been further shown to be advantageous for temporal and spatial control of drug release and deposition in the scaffolds, with a potential to repair bone defect more precisely and effectively. Changes in the BG content resulted in distinct macroscopic form stability and mechanical properties to scaffolds. An increase in the BG content in scaffolds led to less volume swell as well as higher ultimate strength and compressive modulus, which makes the scaffolds mechanically adjustable according to certain structures and properties of different bone defect sites. The developed scaffolds may show promise for promoting bone tissue regeneration.

In tissue engineering, biomaterials are used as scaffolds for spatial distribution of specific cell types. Biomaterials can potentially influence cell proliferation and extracellular matrix formation, both in positive and negative ways. The aim of the present study was to investigate and compare mineralized matrix production of human dental pulp stem cells (DPSC), cultured on 17 different well-characterized polymers. Osteogenic differentiation of DPSC was induced for 21 days on biomaterials using dexamethasone, L-ascorbic-acid-2-phosphate, and sodium β-glycerophosphate. Success of differentiation was analyzed by quantitative RealTime PCR, alkaline phosphatase (ALP) activity, and visualization of calcium accumulations by alizarin red staining with subsequent quantification by colorimetric method. All of the tested biomaterials of an established biomaterial bank enabled a mineralized matrix formation of the DPSC after osteoinductive stimulation. Mineralization on poly(tetrafluoro ethylene) (PTFE), poly(dimethyl siloxane) (PDMS), Texin, LT706, poly(epsilon-caprolactone) (PCL), polyesteramide type-C (PEA-C), hyaluronic acid, and fibrin was significantly enhanced (p<0.05) compared to standard tissue culture polystyrene (TCPS) as control. In particular, PEA-C, hyaluronic acid, and fibrin promoted superior mineralization values. These results were confirmed by ALP activity on the same materials. Different biomaterials differentially influence the differentiation and mineralized matrix formation of human DPSC. Based on the present results, promising biomaterial candidates for bone-related tissue engineering applications in combination with DPSC can be selected.

Transcatheter aortic valve implantation (TAVI) has become a popular alternative technique to surgical valve replacement for critical patients. Biological valve tissue has been used in TAVI procedures for over a decade, with over 150,000 implantations to date. However, with only 6 years of follow up, little is known about the long-term durability of biological tissue. Moreover, the high cost of tissue harvesting and chemical treatment procedures favor the development of alternative synthetic valve leaflet materials. In that context, textile polyester [polyethylene terephthalate (PET)] could be considered as an interesting candidate to replace the biological valve leaflets in TAVI procedures. However, no result is available in the literature about the behavior of textile once in contact with biological tissue in the valve position. The interaction of synthetic textile material with living tissues should be comparable to biological tissue. The purpose of this preliminary work is to compare the in vivo performances of various woven textile PET valves over a 6-month period in order to identify favorable textile construction features. In vivo results indicate that fibrosis as well as calcium deposit can be limited with an appropriate material design.

Time-consuming design and manufacturing processes are a serious disadvantage when adapting human cardiovascular implants as they cause unacceptable delays after the decision to intervene surgically has been made. An ideal cardiovascular implant should have a broad range of characteristics such as strength, viscoelasticity and blood compatibility. The present research proposes the sequence of the geometrical adaptation procedures and presents their results. The adaptation starts from the identification of a person’s current health status while performing abdominal aortic aneurysm (AAA) imaging, which is a point of departure for the mathematical model of a cardiovascular implant. The computerized tomography scan shows the patient-specific geometry parameters of AAA and helps to create a model using COMSOL Multiphysics software. The initial parameters for flow simulation are taken from the results of a patient survey. The simulation results allow choosing the available shape of an implant which ensures a non-turbulent flow. These parameters are essential for the design and manufacturing of an implant prototype which should be tested experimentally for the assurance that the mathematical model is adequate to a physical one. The article gives a focused description of competences and means that are necessary to achieve the shortest possible preparation of the adapted cardiovascular implant for the surgery.

Hydroxyapatite (HA)-based biografts with selenium (Se) and silver (Ag) substitutions were synthesized using the sol-gel method. The synthesized HA-based biografts at various Se and Ag quantity ratios (wt%) were characterized via Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDX). Escherichia coli (JM103) and Gram-positive Staphylococcus aureus (ATCC29293) bacteria were used for the cell viability tests by performing the MTT assay. During antibacterial tests, it was determined that the synthesized biografts showed significant antimicrobial activity on E. coli and S. aureus; however, some materials were effective on Gram-negative E. coli , but had no effect on Gram-positive S. aureus . In vitro cell viability tests revealed that some of the synthesized biografts such as H30Ag10Se15 and H40Ag20Se10 provided the highest cell viability rates compared to those in the control group.

Stereo-electroencephalography depth electrodes, regularly implanted into drug-resistant patients with focal epilepsy to localize the epileptic focus, have a low channel count (6–12 macro- or microelectrodes), limited spatial resolution (0.5–1 cm) and large contact area of the recording sites (~mm 2 ). Thus, they are not suited for high-density local field potential and multiunit recordings. In this paper, we evaluated the long-term electrophysiological recording performance and histocompatibility of a neural interface consisting of 32 microelectrodes providing a physical shape similar to clinical devices. The cylindrically-shaped depth probes made of polyimide (PI) were chronically implanted for 13 weeks into the brain of rats, while cortical or thalamic activity (local field potentials, single-unit and multi-unit activity) was recorded regularly to monitor the temporal change of several features of the electrophysiological performance. To examine the tissue reaction around the probe, neuron-selective and astroglia-selective immunostaining methods were applied. Stable single-unit and multi-unit activity were recorded for several weeks with the implanted depth probes and a weak or moderate tissue reaction was found around the probe track. Our data on biocompatibility presented here and in vivo experiments in non-human primates provide a strong indication that this type of neural probe can be applied in stereo-electroencephalography recordings of up to 2 weeks in humans targeting the localization of epileptic foci providing an increased spatial resolution and the ability to monitor local field potentials and neuronal spiking activity.

Previous studies have shown smooth muscle induction in adipose-derived mesenchymal stem cells (ASCs) caused by long-term cyclic stretch. Here we examined the capability of the short-term straining with time steps of 4, 8, 16 and 24 h alone or combined with TGF-β 1 on smooth muscle induction of rabbit ASCs. Alterations in cell morphology were quantified through the cell shape index and orientation angle, and expression levels of α- SMA , SM22- α, h-caldesmon and calponin3 markers were examined using the real-time polymerase chain reaction (PCR) method. Moreover, F-actin cytoskeleton organization was observed by fluorescence staining. Mechanical strain either alone or combined with growth factor treatment caused significant up-regulation of both early and intermediate smooth muscle cells (SMCs) specific markers during the initial hours of stimulation peaking in 8 to 16 h. Furthermore, gradual alignment of cells perpendicular to the strain direction during loading time, and cell elongation resembling contractile SMC phenotype, together with alignment and reorganization of F-actin fibers were observed. Considering previously reported protein up-regulation in following days of straining, the effects of short-term cyclic stretch on smooth muscle induction of ASCs were revealed which can be helpful in achieving functional contractile SMCs through synergistic mechano-chemical regulation of ASCs as an appealing cell source for vascular tissue engineering.

Failure rates of 2–10% provide evidence for further development in knee arthroplasty. The purpose of our study was to examine the safety of the tibial component of a novel all-ceramic total knee replacement (TKR) (BPK-S Integration ceramic) consisting of BIOLOX ® delta ceramic. The standards ISO 14879-1 and ASTM F1800-07 describe the test set-up for the experimental strength verification with a significantly increased maximum load of 5300 N (900 N are required) and post-fatigue burst strength testing. All specimens were able to prove their mechanical strength against fracture in the alternating load test. There was no material fracture in any of the included tibial components. The subsequent post-fatigue burst strength testing revealed the maximum strength against fracture of all specimens. With at least 9.7 kN for size 3 and at least 12.1 kN for size 6, all specimens showed relatively large strength reserves to the stress in the alternating load test. So far we simulated an in vivo lifetime of 10 years for the tibial component. Further studies should be conducted in which longer in vivo lifetimes of the components are simulated to investigate possible fatigue of the used material over a longer period of time.

Transcatheter aortic valve implantation (TAVI) is nowadays a popular alternative technique to surgical valve replacement for critical patients. Biological valve tissue has been used in these devices for over a decade now with over 100,000 implantations. However, material degradations due to crimping for catheter insertion purpose have been reported, and with only 6-year follow-up, no information is available about the long-term durability of biological tissue. Moreover, expensive biological tissue harvesting and chemical treatment procedures tend to promote the development of synthetic valve leaflet materials. Textile polyester (PET) material is characterized by outstanding folding and strength properties combined with proven biocompatibility and could therefore be considered as a candidate to replace biological valve leaflets in TAVI devices. Nevertheless, the material should be preferentially partly elastic in order to limit water hammer effects at valve closing time and prevent exaggerated stress from occurring into the stent and the valve. The purpose of the present work is to study in vitro the mechanical as well as the hydrodynamic behavior of a hybrid elastic textile valve device combining non-deformable PET yarn and elastic polyurethane (PU) yarn. The hybrid valve properties are compared with those of a non-elastic textile valve. Testing results show improved hydrodynamic properties with the elastic construction. However, under fatigue conditions, the interaction between PU and PET yarns tends to limit the valve durability.